ABSTRACT The overuse of low-value health services (i.e., a health service whose immediate or downstream costs or harms exceed its benefits) is a major driver of wasteful healthcare spending in the United States. Existing low- value health service metrics have incorporated tests and procedures, but not medications. Thus, low-value pre- scribing has not been systematically studied. There is an urgent need to accurately characterize and reduce low-value prescribing in adults aged ?65 years, as 2 in 5 have been prescribed ?5 medications (i.e., polyphar- macy), resulting in adverse drug events, unnecessary out-of-pocket costs, and hospitalizations. The Choosing Wisely Campaign has published recommendations against some low-value prescribing practices. However, these recommendations have not been operationalized for use in administrative data and were developed with- out incorporating patients? perspectives on healthcare value. Thus, there is no metric that consolidates and streamlines existing recommendations and incorporates the perspectives of patients, prescribers, and payers to clearly define and systematically measure low-value prescribing. A claims-based metric that incorporates the input of diverse stakeholders will enable health systems and payers to easily measure low-value prescribing in older adults and develop policies and interventions to reduce such prescribing without compromising quality or patient satisfaction. The overarching objective of this mentored career development award is to develop, vali- date, and apply a metric that will accurately characterize specific low-value prescribing practices using admin- istrative data and reflect the perspectives and beliefs of patients, prescribers, and payers as they relate to healthcare value. To achieve this objective, we will complete the following Specific Aims: 1) To identify and de- fine key low-value prescribing practices from the perspective of diverse stakeholders to incorporate in the low- value prescribing metric; 2) To validate the components of the low-value prescribing metric for use in adminis- trative data; 3) To determine the patient, provider, and geographic factors associated with low-value prescrib- ing. Completion of these Aims will provide key evidence regarding the prevalence of, factors associated with, and prescribers incentives to engage in low-value prescribing, and will empower health systems, payers, and policy makers to further study and reduce such prescribing in a way that is clinically sound and acceptable to patients and prescribers. To complete my training, I require additional training in qualitative research, phar- macoepidemiology, and the design and implementation of health service interventions. This will enable me to successfully compete for NIH R-series grants to lead studies evaluating the impact of low-value prescribing on patient-centered outcomes and to pilot and implement a health service intervention to mitigate low-value pre- scribing in older adults using the proposed metric. The skills and experience I will obtain through this K23 Award will enable me to become an independent clinician-investigator, committed to furthering the mission of the NIA by ensuring that older adults receive high-value care across the full spectrum of health services.